The present invention relates generally to wireless receivers, and more particularly to processing delay allocation for multi-carrier receivers that receive multi-path signals.
Wireless signals often travel multiple propagation paths between a transmitter and an intended receiver. As a result, the intended receiver receives a composite signal that includes multiple images of a transmitted signal, where each image generally experiences different path delay, phase, and attenuation effects. Different signal images therefore arrive at the receiver at different times, causing a delay spread between the received signal images. The maximum delay spread between signal images depends on, among other things, the differing characteristics of the signal propagation paths.
Because the signal energy is distributed among the multiple signal images, wireless devices often use a receiver that combines the received signal images to improve the signal-to-noise ratio (SNR) of the output signal, e.g., a RAKE receiver. RAKE receivers include a plurality of RAKE fingers tuned to different delays to despread signal images. Typically, the RAKE receiver tunes its available RAKE fingers to the strongest signal images, such that each selected signal image is despread, weighted, and subsequently combined with the other selected and despread signal images. Combining multiple signal images in this manner generally improves the SNR of the received signal.
To improve wireless data rates, wireless communication systems may also use different frequency carriers for different users. To compensate for multi-path propagation issues associated with each carrier, receivers in such multi-carrier systems may include one RAKE receiver subsystem for each carrier, where each RAKE receiver subsystem includes a fixed number of RAKE fingers. Ideally, each RAKE receiver subsystem includes enough fingers to adequately process the received signal for the corresponding carrier. However, because receiver complexity increases as the number of RAKE fingers increases, the ideal RAKE finger distribution is not always possible.